Insects - Pests of Ornamental Trees, Shrubs and Flowers - page 87

Family ADELGIDAE

Thelaxes dryophila (Schrank) ( 178 )
syn. T. quercicola Westwood
Generally common on oak ( Quercus ), and often
abundant on young trees. Eurasiatic. Widely distributed
in Europe.

Conifer-feeding, aphid-like insects but, unlike true
aphids, with short antennal segments, reduced wing
venation, no siphunculi and entirely oviparous females;
alates have five antennal segments. Lifecycles are very
complex, and often involve a variety of different
morphs and alteration of host plant.

DESCRIPTION
Apterous female: 2.2-2.8 mm long; reddish brown to
green, with marked segmentation and a pale dorsal line;
body flattened and hairy, and lightly dusted with whitish
wax; eyes small, antennae short, siphunculi reduced to
flat cones, and cauda knob-like.

Adelges abietis (Linnaeus) ( 179-180 )
A spruce pineapple-gall adelges
An often abundant pest of spruce ( Picea ), and
commonly damaging to ornamentals, including Norway
spruces ( P. abies ) grown as Christmas trees. Present
throughout the natural range of spruces and widely
introduced with such plants to many other areas.

LIFE HISTORY
Overwintered eggs hatch in the spring. Dense colonies
of wingless aphids then develop on the young shoots
and underside of oak leaves. Winged aphids arise in the
summer, and these readily spread infestations from tree
to tree. Sexual forms appear in August, mated females
eventually depositing winter eggs. The aphids produce
copious quantities of honeydew, and colonies are
strongly ant-attended.

DESCRIPTION
Apterous female (pseudo-fundatrix): yellowish green
to light green, with 5-segmented antennae and five pairs
of abdominal spiracles. Alate female (gallicola):
1.8-2.2 mm long; yellow, with 5-segmented antennae;
fore wings 2.5-2.8 mm long.

DAMAGE
Vigour of heavily infested shoots is reduced, and
persistent infestations on young trees are of particular
significance.

LIFE HISTORY
This adelgid spends its life on one host, inhabiting
characteristic pineapple-like galls on the young shoots
of Norway spruce. The galls vary considerably in size,
those on the vigorous young shoots usually being the
largest, but are most frequently about 15-20 mm long.
In this species the number of adult morphs is restricted
to just two: wingless pseudo-fundatrices and winged
gallicolae. Gallicolae escape from mature galls during
the late summer, usually during August and September,
and then deposit eggs. These hatch into nymphs which
overwinter close to the buds. In the spring the nymphs

179 180

179 Gall of spruce pineapple-gall adelges ( Adelges abietis )
on Picea .

180 Colony of spruce pineapple-gall adelges ( Adelges abietis ).